Method of Electrically Isolating Leads of a Lead Frame Strip

ABSTRACT

A lead frame strip includes a plurality of connected unit lead frames, each unit lead frame having a die paddle and a plurality of leads connected to a periphery of the unit lead frame. The lead frame strip is processed by attaching a semiconductor die to each of the die paddles and covering the unit lead frames with a molding compound after the semiconductor dies are attached to the die paddles. Spaced apart cuts are formed in the periphery of each unit lead frame that sever the leads from the periphery of each unit lead frame and extend at least partially into the molding compound in regions of the periphery where the leads are located so that the molding compound remains intact between the cuts. The lead frame strip is processed after the cuts are formed, and the unit lead frames are later separated into individual packages.

TECHNICAL FIELD

The instant application relates to lead frame strips, and moreparticularly to electrical isolation of the leads of a lead frame stripduring lead frame strip processing.

BACKGROUND

A lead frame forms the base or skeleton of an IC package, providingmechanical support to semiconductor dies during assembly into a finishedpackage. A lead frame typically includes a die paddle for attaching asemiconductor die, and leads providing the means for external electricalconnection to the die. The die can be connected to the leads by wires,e.g. through wire bonding or tape automated bonds. Lead frames aretypically constructed from flat sheet metal, e.g. by stamping oretching. The sheet metal is typically exposed to chemical etchants thatremove areas not covered by photoresist. After the etching process, theetched frames are singulated (separated) into lead frame strips. Eachlead frame strip includes a number of unit lead frames each having thedie paddle and lead construction described above.

Semiconductor dies attached to the die paddles after completion of theassembly process of a lead frame strip are usually tested afterseparation of the unit lead frames from the lead frame strip, e.g. bypunching. Alternatively, the unit lead frames remain mechanicallyconnected to the lead frame strip by tie bars during die testing. Thisis commonly referred to as lead frame strip testing. Separation of theunit lead frames from the lead frame strip occurs after electricaltesting. However, the devices must be electrically isolated from oneanother during lead frame strip testing. Conventional processinginvolves cutting about half-way through the entire periphery of eachunit lead frame to sever the leads, leaving a thin part of moldingcompound intact in the periphery to hold the units in place during leadframe strip testing. However, such processing increases wearing of thesawing blade which can cause inaccuracy. Also, rigidity of the leadframe strip decreases after the half-cut process, especially for thinpackages. In addition a long cycle time is needed to perform thehalf-cut on the entire lead frame strip, increasing the cost of theindividual packages produced from the lead frame strip.

SUMMARY

A lead frame strip includes a plurality of connected unit lead frames,each unit lead frame having a die paddle and a plurality of leadsconnected to a periphery of the unit lead frame. According to anembodiment of a method of processing the lead frame strip, the methodcomprises: attaching a semiconductor die to each of the die paddles;covering the unit lead frames with a molding compound after thesemiconductor dies are attached to the die paddles; forming spaced apartcuts in the periphery of each unit lead frame that sever the leads fromthe periphery of each unit lead frame and extend at least partially intothe molding compound in regions of the periphery where the leads arelocated so that the molding compound remains intact between the cuts;and processing the lead frame strip after the cuts are formed in theperiphery of each unit lead frame.

The unit lead frames can be arranged in a plurality of rows and columnswith the leads extending toward the die paddles along two opposing sidesof the die paddles. According to this embodiment, the method ofprocessing the lead frame strip comprises: attaching a semiconductor dieto each of the die paddles; covering the unit lead frames with a moldingcompound after the semiconductor dies are attached to the die paddles;cutting a single line extending horizontally through the periphery ofthe unit lead frames between the rows to sever the leads from theperiphery of each unit lead frame; processing the lead frame strip aftercutting the single line between adjacent rows of the unit lead frames;and cutting a single line extending vertically through the periphery ofthe unit lead frames between the columns after the processing of thelead frame strip to separate the unit lead frames into individualpackages.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1 illustrates a plan view of a lead frame strip with regionstargeted for cutting to sever the leads of the lead frame strip,according to an embodiment.

FIG. 2, which includes FIGS. 2A through 2D, illustrates different stagesof an embodiment of a method of severing the leads of a lead frame stripusing a pressurized liquid stream.

FIG. 3, which includes FIGS. 3A through 3D, illustrates different stagesof another embodiment of a method of severing the leads of a lead framestrip using a pressurized liquid stream.

FIG. 4 illustrates a plan view of a mask placed on a lead frame stripwith cutouts that expose regions targeted for cutting to sever the leadsof the lead frame strip, according to an embodiment.

FIG. 5 illustrates a plan view of a lead frame strip with regionstargeted for cutting to sever the leads of the lead frame strip,according to another embodiment.

FIG. 6, which includes FIGS. 6A through 6D, illustrates different stagesof an embodiment of a method of severing the leads of a lead frame stripusing a laser beam.

FIG. 7, which includes FIGS. 7A through 7D, illustrates different stagesof another embodiment of a method of severing the leads of a lead framestrip using a laser beam.

FIG. 8, which includes FIGS. 8A and 8B, illustrates different stages ofan embodiment of a method of severing the leads of a lead frame striphaving rows and columns of unit lead frames with the leads extendingtoward die paddles of the unit lead frames along two opposing sides ofthe die paddles.

DETAILED DESCRIPTION

According to embodiments described herein, spaced apart cuts are formedaround the periphery of each unit lead frame of a lead frame strip toelectrically isolate the leads for subsequent processing such as leadframe strip testing, partial plating, electrical charging, etc. Amolding compound encapsulating the unit lead frame remains at leastpartly intact between the cuts to provide rigidity to the lead framestrip during the subsequent processing. The unit lead frames are laterseparated from the lead frame strip into individual packages.

FIG. 1 illustrates a top plan view of part of a lead frame strip 100according to an embodiment. The lead frame strip 100 includes aplurality of connected unit lead frames 102, two of which are shown inFIG. 1. Each unit lead frame 102 has a die paddle 104 for attaching oneor more semiconductor dies 106, tie bars 108 connecting the die paddle104 to the periphery 110 of the unit lead frame 102, and a plurality ofleads 112 projecting from the periphery 110 toward the die paddle 104.The boxes labeled 114 in FIG. 1 represent the final size of theindividual packages to be later produced upon separation from the leadframe strip 100.

In one embodiment, the lead frame strip 100 is constructed from flatsheet metal, e.g. by stamping or etching. For example, the sheet metalcan be exposed to chemical etchants that remove areas not covered byphotoresist. Other processing can be performed, e.g. laser etching topattern the sheet metal. After the patterning process, the patternedframes are singulated (separated) into lead frame strips. One such leadframe strip 100 is shown in FIG. 1.

Electrical connections (not shown for ease of illustration) are formedbetween the leads 112 of each unit lead frame 102 and terminals of thesemiconductor dies 106 attached to the die paddles 104. The unit leadframes 102 and the semiconductor dies 106 are then encapsulated with amolding compound to form individual packages. The molding compound isnot shown in FIG. 1 for ease of illustration. More than one die paddle104 can be included in each individual package, and the individualpackages are later physically separated into individual units.

Prior to testing of the semiconductor dies 106 attached to the diepaddles 104 or other processing such as partial plating, electricalcharging, etc., spaced apart cuts are formed in the periphery 110 ofeach unit lead frame 102 of the lead frame strip 100 to electricallyisolate the leads 112 of each unit lead frame 102 for subsequentprocessing. The regions to be cut are labeled 116 in FIG. 1.

FIG. 2, which includes FIGS. 2A through 2D, illustrates an embodiment ofa method of forming the spaced apart cuts in the periphery 110 of eachunit lead frame 102 of the lead frame strip 100. FIG. 2A shows across-sectional view of part of a unit lead frame 102 in the periphery110 where a lead 112 is located. The side 113 of the lead 112 uncoveredby a molding compound 120 can be plated 122 e.g. with silver, tin,palladium, etc. The other sides of the lead 112 and the unit lead frames102 of the lead frame strip 100, including the semiconductor dies 106attached to the die paddles 104 of the lead frame strip 100, are coveredby the molding compound 120.

FIG. 2B shows the lead 112 during the cutting process. According to thisembodiment, spaced apart cuts 124 are formed in the periphery 110 ofeach unit lead frame 102 by directing a pressurized liquid stream 126 atthe regions 116 of the periphery 110 of each unit lead frame 102 wherethe leads 112 are located to cut through the leads 112 and the moldingcompound 120 in these regions 116.

More particularly, a water cutting tool includes a high pressure waterinlet 128, a jewel 130 such as ruby or diamond, an inlet 132 for addingan abrasive, and a mixing tube 134 for producing a cohesive liquid mixof high-pressure water and abrasive. The pressurized liquid stream 126is directed at the regions 116 of the periphery 110 of each unit leadframe 102 where the leads 112 are located to cut through the leads 112and the molding compound 120 in these regions 116 via the pressurizedliquid stream 126. Movement of the water cutting tool is controlled by acontroller 136. The controller 136 is programmed to move the watercutting tool in x and y directions and control the rate of movement. Inone embodiment, the rate of movement of the water cutting tool is variedaround the periphery 110 of each unit lead frame 102 so that thepressurized liquid stream 126 is directed at the regions 116 of theperiphery 110 where the leads 112 are located for a longer period oftime than in other regions around the periphery 110. As a result, theleads 112 and the molding compound 120 are cut through in the regions116 of the periphery 110 where the leads 112 are located and the moldingcompound 120 remains at least partly intact in other regions around theperiphery 110 to provide rigidity during subsequent processing of thelead frame strip 100. The spaced apart cuts 124 can also act as a stressrelief mechanism for reducing warpage of the lead frame strip 100 duringhandling.

FIG. 2C shows one embodiment of such processing, in which the severedleads 112 are contacted by probes 138 to test the semiconductor dies 106attached to the die paddles 104 of the unit lead frames 102. Because theleads 112 have been severed from the periphery 100 of the respectiveunit lead frames 102 by a pressurized liquid stream 126, thesemiconductor dies 106 can be tested in parallel using any standard leadframe strip testing methodology without interference between the dies106. The molding compound 120 remains at least partly intact between thecuts 124 so that the lead frame strip 100 remains solid and robust forhandling.

FIG. 2D shows the severed lead 112 during a sawing process in which theentire periphery 110 of each unit lead frame 102 is cut by a saw blade140 after testing of the lead frame strip 100, to separate the unit leadframes 102 into individual package units. Conventional saw bladestypically have a width (Wsaw) of at least 0.3 mm and more typicallyabout 0.45 mm. The spaced apart cuts 124 formed in the periphery 110 ofeach unit lead frame 102 by the pressurized liquid stream 126 have awidth (Wcut) of 0.25 mm or less e.g. down to a minimum of 0.12 mm. Assuch, the width (Wcut) of the cuts 124 made by the pressurized liquidstream 126 is narrower than the width (Wsaw) of the saw blade 140.Severing the leads 112 with such narrower cuts 124 yields additionallead area for contacting by the test probes 138 during lead frame striptesting as compared to severing the leads 112 using a saw blade. This isparticularly beneficial for power devices subjected to high currentkelvin testing e.g. where two probes per pad are used as shown in FIG.2C. Also, the use of a water cutting tool instead of a saw blade tosever the leads 112 for lead frame strip testing or other processingreduces saw blade wear and tear, yielding more constant and accuratelead frame strip processing and faster process time due to cutting onlyselected regions 116 instead of the entire periphery 110 of each unitlead frame 102.

FIG. 3, which includes FIGS. 3A through 3D, illustrates anotherembodiment of a method of forming the spaced apart cuts 124 in theperiphery 110 of each unit lead frame 102 of the lead frame strip 100.FIG. 3A shows a cross-sectional view of part of a unit lead frame 102 inthe periphery 110 where a lead 112 is located, FIG. 3B shows the lead112 during the water cutting process, FIG. 3C shows the severed lead 112during testing, and FIG. 3D shows the severed lead 112 during a sawingprocess which separates the unit lead frames 102 into individual packageunits. The embodiment shown in FIG. 3 is similar to the embodiment showin FIG. 2, however, the pressurized liquid stream 126 is controlled suchthat the cuts 124 sever the leads 112 in the targeted regions 116 of theperiphery 110 of each unit lead frame and extend only partially into themolding compound 120 in these regions 116 so that the molding compound120 remains partly intact below the cuts 124. In one embodiment, therate of movement of the water cutting tool is controlled so that themolding compound 120 is not cut through in the cut regions 116.

FIG. 4 illustrates a top plan view of the part of the lead frame strip100 shown in FIG. 1, with a mask 200 placed on the lead frame strip 100prior to severing of the leads 112 by a pressurized liquid stream 126.The mask 200 covers the unit lead frames 102 and is made of a relativelyhard material such as carbonite or ceramic. The mask 200 has cutouts 202over the regions 116 of the periphery 110 of each unit lead frame 102where the leads 112 are located, so that the pressurized liquid stream126 is blocked from cutting regions of the molding compound 120protected by the mask 200. The mask 200 can be used in addition to, orinstead of, varying the rate of movement of the water cutting tool bythe controller 136. Without the mask 200, the rate of movement of thewater cutting tool is varied as previously described herein to ensurethat the molding compound 120 is not cut completely through by thepressurized liquid stream 124 in regions not covering the leads 112.Otherwise, the entire periphery 110 of each unit lead frame 102 would becut completely through by the pressurized liquid stream 126 and thestability of the lead frame strip 100 would be significantly reduced.With the mask 200, the variable rate control of the movement of thewater cutting tool can be optionally implemented or instead omitted.With both variable rate control of the pressurized liquid stream 124 andthe mask 200, the pressurized liquid stream 126 is directed at thecutouts 202 in the mask 200 for a longer period of time than at the mask200.

FIG. 5 illustrates a top plan view of part of a lead frame strip 100according to another embodiment. The embodiment shown in FIG. 5 issimilar to the embodiments shown in FIGS. 1 through 4, however, thespaced apart cuts 124 are formed in the periphery 110 of each unit leadframe 102 of the lead frame strip 100 using a laser beam to electricallyisolate the leads 112 for subsequent processing. The regions to be cutby laser beam are labeled 300 in FIG. 1. Smaller regions 300 aretargeted for laser beam cutting as compared to FIG. 1, leaving more ofthe molding compound 120 intact post severing of the leads 112.

FIG. 6, which includes FIGS. 6A through 6D, illustrates an embodiment ofa method of forming the spaced apart cuts 124 in the periphery 110 ofeach unit lead frame 102 of the lead frame strip 100 using a laser beam302. FIG. 6A shows a cross-sectional view of part of a unit lead frame102 in the periphery 110 where a lead 112 is located. The side 113 ofthe lead 112 uncovered by the molding compound 120 can be plated 122e.g. with silver, tin, palladium, etc. The other sides of the lead 112and the unit lead frames 102 of the lead frame strip 100, including thesemiconductor dies 106 attached to the die paddles 104, are covered by amolding compound 120.

FIG. 6B shows the lead during the cutting process. According to thisembodiment, the spaced apart cuts 124 are formed in the periphery 110 ofeach unit lead frame 102 by directing a laser beam 302 at the regions300 of the periphery 110 of each unit lead frame 102 where the leads 112are located to cut through the leads 112 and at least part of themolding compound 120 in these regions 300.

More particularly, a laser cutting tool includes a laser 304 forgenerating and directing a laser beam 302 towards the lead frame strip100. The laser beam 302 is directed at the regions 300 of the periphery110 of each unit lead frame 102 where the leads 112 are located to cutthrough the leads 112 and at least some of the molding compound 120 inthese regions 300 via the laser beam 302. Movement of the laser 304 iscontrolled by a controller 306. The controller 306 is programmed to movethe laser 304 in x and y directions and control the lasing operation sothat the laser beam 302 is directed only at the regions 300 of theperiphery 110 where the leads 112 are located. As a result, the leads112 are cut through and at least some of the molding compound 120removed in the targeted regions 300 of the periphery 110 where the leads112 are located. The molding compound 120 remains completely intact inother regions around the periphery between the cuts 124 to providerigidity during subsequent processing of the lead frame strip 100.

FIG. 6C shows one embodiment of post-lasing processing, in which thesevered leads 112 are contacted by probes 138 to test the semiconductordies 106 attached to the die paddles 104 of the unit lead frames 102.Because the leads 112 have been severed at the periphery 110 of therespective unit lead frames 102 by the laser tool, the semiconductordies 106 can be tested in parallel using any standard lead frame striptesting methodology without interference between the dies 106. Themolding compound 120 remains fully intact between the cuts 124 so thatthe lead frame strip remains solid and robust during handling.Optionally, the molding compound 120 in these regions between the cuts124 can be partly lased to remove some of the molding compound 120 inorder to reduce warpage of the lead frame strip 100 during subsequenthandling.

FIG. 6D shows the lead 112 during a sawing process in which the entireperiphery 110 of each unit lead frame 102 is cut by a saw blade 140after testing of the lead frame strip testing, to separate the unit leadframes 102 into individual package units. The spaced apart cuts 124formed in the periphery 110 of each unit lead frame 102 by the laserbeam 302 have a width (Wcut) of 0.25 mm or less e.g. down to 0.12 mm orless depending on the type of laser cutting tool. As such, the width(Wcut) of the cuts 124 made in the periphery 110 of each unit lead frame102 by the laser beam 302 is narrower than the width (Wsaw) of the sawblade 140. This yields additional lead area for contacting by the probes138 during lead frame strip testing as previously described herein.

FIG. 7, which includes FIGS. 7A through 7D, illustrates anotherembodiment of a method of forming the spaced apart cuts 124 in theperiphery 110 of each unit lead frame 102 of the lead frame strip 100using a laser beam 302. FIG. 7A shows a cross-sectional view of part ofa unit lead frame 102 in the periphery 110 where a lead 112 is located,FIG. 7B shows the lead 112 during the laser cutting process, FIG. 7Cshows the severed lead 112 during testing, and FIG. 7D shows the severedlead during a sawing process which separates the unit lead frames 102into individual package units. The embodiment shown in FIG. 7 is similarto the embodiment show in FIG. 6, however, the molding compound 120 iscut through instead of partly removed in the regions 300 of theperiphery 110 where the lasing occurs according to this embodiment. Theamount of molding compound 120 lased in the targeted regions 300 can becontrolled by the power level, focal point and length of lasing. Thecontroller 306 can be programmed to precisely control one or more ofthese parameters so that the desired regions 300 and materials are lasedto sever the leads 112, including cutting through the molding compound120 in these regions 300.

Each of the embodiments previously described herein relates to severingthe leads 112 from the periphery 110 of unit lead frames 102 of a leadframe strip 100 to ensure proper electrical isolation of the leads 112e.g. during lead frame strip testing. In some packages, the die paddles104 should also be disconnected from the periphery 110 by severing thetie bars 108 that attach the die paddles 104 to the periphery 110 toensure complete electrical isolation of individual packages during leadframe strip testing. Otherwise, the die paddles 104 remain electricallyconnected to the lead frame strip 100 by the tie bars 108 duringtesting. This is problematic for applications where the die paddles 104serve an electrical connection function, e.g. in DSO (dual smalloutline) packages where the exposed die paddles 104 provide anelectrical connection to the backside of semiconductor dies 106 attachedto the die paddles 104.

In this case, the tie bars 108 electrically short the die paddles 104 tothe lead frame strip 100 and to other die paddles 104 attached to thesame lead frame strip 100, complicating the electrical testing process.Electrical isolation may also be required for other lead frameprocessing such as partial plating and electrical charge processes. Assuch, the regions 116/300 targeted for cutting e.g. by a pressurizedliquid stream 126 or laser beam 302 as previously described herein caninclude both the leads 112 and the tie bars 108 as shown in FIGS. 1 and5. The cutting process employed severs both the leads 112 and the tiebars 108 in the targeted regions 116/300 according to this embodiment,completely electrically isolating the packages from one another. Thelead frame strip 100 is then subsequently processed e.g. by lead framestrip testing, partial plating, electrical charging, etc. after the tiebars 108 are severed by the additional cuts.

FIG. 8, which includes FIGS. 8A and 8B, illustrates yet anotherembodiment of severing the leads 112 of a lead frame strip 100 toprovide electrical isolation during subsequent processing of the leadframe strip 100. According to this embodiment, the unit lead frames 102are arranged in a plurality of rows and columns with the leads 112extending toward the die paddles 104 along two opposing sides of the diepaddles 104. After the unit lead frames 102 with the semiconductor dies(not shown in FIG. 8 for ease of illustration) are covered with amolding compound (also not shown in FIG. 8 for ease of illustration), asingle line 400 extending horizontally through the periphery 110 of eachunit lead frame 102 is cut between the rows to sever the leads 112 fromthe periphery 110 of the unit lead frames 102 as shown in FIG. 8A. Thehorizontal cutting regions are labeled 400 in FIG. 8A.

In one embodiment, the single lines 400 extending horizontally throughthe periphery 110 of the unit lead frames 102 between the rows are cutby directing a pressurized liquid stream 126 in a single line extendinghorizontally between the rows as previously described herein. A mask 200may or may not be used also as previously described herein. In anotherembodiment, the single lines 400 extending horizontally through theperiphery 110 of the unit lead frames 102 between the rows are cut bysawing along a single line extending horizontally between the rows usinga saw blade 140. In either case, the lead frame strip 100 is thensubsequently processed e.g. by lead frame strip testing, partialplating, electrical charging, etc. after cutting the single lines 400between adjacent rows of the unit lead frames 102.

After this processing, a single line 402 extending vertically throughthe periphery 110 of the unit lead frames 102 is cut between the columnsto separate the unit lead frames 102 into individual package units. Thevertical cutting regions are labeled 402 in FIG. 8B. In one embodiment,the single lines 400 extending horizontally through the periphery 110 ofthe unit lead frames 102 and the single lines 402 extending verticallythrough the periphery 110 of the unit lead frames 102 are cut using asaw blade. In another embodiment, the single lines 400 extendinghorizontally through the periphery 110 of the unit lead frames 102 arecut using a pressurized liquid stream 126 and the single lines 402extending vertically through the periphery 110 of the unit lead frames102 between the columns are cut using a saw blade 140 having a widerwidth than the single lines 400 formed by the pressurized liquid stream126.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first”, “second”, and the like, are also used to describevarious elements, regions, sections, etc. and are also not intended tobe limiting. Like terms refer to like elements throughout thedescription.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open-ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

1. A method of processing a lead frame strip including a plurality ofconnected unit lead frames, each unit lead frame having a die paddle anda plurality of leads connected to a periphery of the unit lead frame,the method comprising: attaching a semiconductor die to each of the diepaddles; covering the unit lead frames with a molding compound after thesemiconductor dies are attached to the die paddles; forming spaced apartcuts in the periphery of each unit lead frame that sever the leads fromthe periphery of each unit lead frame and extend at least partially intothe molding compound in regions of the periphery where the leads arelocated so that the molding compound remains intact between the cuts,wherein the spaced apart cuts are formed in the periphery of each unitlead frame by directing a pressurized liquid stream at the regions ofthe periphery of each unit lead frame where the leads are located to cutthrough the leads in these regions; and processing the lead frame stripafter the cuts are formed in the periphery of each unit lead frame. 2.(canceled)
 3. The method of claim 1, further comprising: placing a maskon the lead frame strip that covers the unit lead frames, the maskhaving cutouts over the regions of the periphery of each unit lead framewhere the leads are located so that the pressurized liquid stream isblocked from cutting regions of the molding compound protected by themask.
 4. The method of claim 3, wherein the mask comprises carbonite orceramic.
 5. The method of claim 3, further comprising: varying a rate ofmovement of the pressurized liquid stream around the periphery of eachunit lead frame so that the pressurized liquid stream is directed at thecutouts in the mask for a longer period of time than at the mask.
 6. Themethod of claim 1, further comprising: varying a rate of movement of thepressurized liquid stream around the periphery of each unit lead frameso that the pressurized liquid stream is directed at the regions of theperiphery where the leads are located for a longer period of time thanin other regions around the periphery, to cut through the leads and themolding compound in the regions of the periphery where the leads arelocated and leave the molding compound at least partly intact in theother regions around the periphery.
 7. The method of claim 1, furthercomprising cutting the entire periphery of each unit lead frame afterthe processing of the lead frame strip to separate the unit lead framesinto individual packages.
 8. The method of claim 7, wherein the entireperiphery of each unit lead frame is cut by a saw blade, and wherein awidth of the cuts made in the periphery of each unit lead frame by thepressurized liquid stream is narrower than the width of the saw blade.9. The method of claim 8, wherein the width of the cuts made in theperiphery of each unit lead frame by the pressurized liquid stream is0.25 mm or less and the width of the saw blade is 0.3 mm or greater.10-13. (canceled)
 14. The method of claim 1, wherein processing the leadframe strip after forming the cuts in the periphery of each unit leadframe comprises: testing the semiconductor dies by probing the leadsafter the cuts are formed in the periphery of each unit lead frame. 15.The method of claim 1, further comprising: forming additional spacedapart cuts in the periphery of each unit lead frame that sever tie barsconnecting adjacent ones of the die paddles from the periphery of eachunit lead frame and extend at least partially into the molding compoundin regions of the periphery where the tie bars are located so that themolding compound remains intact between the additional cuts, wherein thelead frame strip is processed after the additional cuts are formed inthe periphery of each unit lead frame. 16-20. (canceled)